The current warfare and terrorist activities around the world necessitate a vastly enhanced defense against potential weapons of mass destruction. Among the most lethal and readily deployed are various Clostridium botulinum neurotoxins (BoNTs), the causative agents of the clinical condition of botulism. Our general program encompasses exploitation of novel phage-displayed human scFv libraries to obtain monoclonal antibodies (mAbs) for protection against BoNTs. We have made substantial progress in this area under our funded NIAID R21-AI53269. One mAb, in Fab format, already prepared, shows neutralizing activity against BoNT A in a cell-based assay. Our primary aim in this application is to develop fully human IgGs able to neutralize BoNTs A and B in a mouse model. Human IgG will be the most suitable format for use in passive immunotherapy and/or prophylaxis against BoNTs and the condition of botulism. To this end, our strategy encompasses: 1) Human anti-BoNT scFvs, currently in hand, will be characterized and converted into the Fab format for an in vitro cytotoxicity assay; 2) The best candidates, in scFv format, will enter molecular evolution protocols to enhance affinity, followed by conversion to Fabs, and retesting; 3) The best candidates will be assembled into fully human IgG for an in vitro cytotoxicity assay; 4) Final Fab and IgG candidates will be entered into mouse toxicity assays to evaluate protection against BoNTs. The proposed research provides a foundation for the use of human IgGs against BoNTs by military personnel during warfare or the general public in the event of bioterrorist activity.